Fuel System Checks

Check for a restricted fuel filter or an incorrect fuel pressure. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article.
Check the fuel injectors. Perform the Fuel Injector Coil Test procedure and the Fuel Injector Balance Test procedure. See FUEL INJECTOR COIL TEST - ENGINE COOLANT TEMPERATURE BETWEEN 50-95°F (10-35°C) and FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article.
Check for water contamination of the fuel.